1. Field of Invention
The present invention relates to a device and a process for manufacturing a film tube. Furthermore, the process aims to provide protection for the film tube itself.
2. Description of the Prior Art
Film tubes are used, among others, in the so-called Form, Fill and Seal Machines, referred to in the following description as FFS machines. These machines are disclosed in the published patents DE 199 33 446, DE 199 20 478 and DE 199 36 660. The FFS machines have unwinding stations on which film tubes are stored. These unwinding stations unwind the film tubes and separate them into film tube segments. Usually in the later process steps, the film tubes are provided with bottoms, the resulting bag is filled with the filling material and the bag is sealed.
Usually, film tubes are formed by blown film extrusion for the purpose of processing using FFS machines. The format of these film tubes (here, their periphery) is in agreement with the bag to be formed subsequently. This approach necessitates the relatively expensive replacement of formats in the blown film extrusion plants for the purpose of realizing different bag formats. Moreover, the formats required for the bag formation are relatively small and hence cannot be manufactured economically. Blown film extrusion plants of bigger format produce the same foil at much lesser costs per unit of area.
Therefore, experiments have been conducted many times with the purpose of first manufacturing very broad film webs by flat film extrusion or by blown film extrusion using machines of a bigger format. Here also, blown film extrusion plants were preferred primarily for cost reasons. The resulting film tubes or film webs of a big format were then processed further into flat film webs by cutting them as per the format required. Subsequently, one of these laid-flat film webs is folded up and joined by a longitudinal joint seam to form a film tube. A disadvantage of such usually very short film tubes is that the thick joint created by the longitudinal joint seam complicates the winding process of the film tube, since the rolled-up film tube tends to telescope, i.e. it assumes a frusticonical shape, due to the addition of the thick joints.
Even film tube segments are produced in a similar manner for the purpose of manufacturing bags of a higher quality. Thus, for instance, the manufacture of side-gusset pouches or side-gusset bags is known from prior art that are formed out of several film segments. For this purpose the edges of each of the film segments are usually sealed together. This process is carried out between sealing jaws that clamp the material to be sealed during the sealing process.
This method necessitates the intermittent conveyance of the tube material during the entire tube-forming process and thus results in extremely low production speeds. Therefore the objective of the present invention is to propose a process that can be executed faster for manufacturing a film tube out of at least one film web.